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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Infinite loop in demangler"
href="https://bugs.llvm.org/show_bug.cgi?id=51407">51407</a>
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<th>Summary</th>
<td>Infinite loop in demangler
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>llvm-c++filt
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>borisov.mikhail@gmail.com
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</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>A libfuzzer run has discovered some inputs for which the demangler does not
terminate.
When minimized, it looks like this: _Zcv1BIRT_EIS1_E
Deciphered:
_Z
cv - conversion operator
* result type
1B - "B"
I - template args begin
R - reference type <.
T_ - forward template reference | *
E - template args end | |
| |
* parameter type | |
I - template args begin | |
S1_ - substitution #1 * <'
E - template args end
The reason is: template-parameter refs in conversion operator result type
create forward-references, while substitutions are instantly resolved via
back-references. Together these can create a reference loop. It causes an
infinite loop in ReferenceType::collapse().
I see three possible ways to avoid these loops:
1. check if resolving a forward reference creates a loop and reject the invalid
input (hard to traverse AST at this point)
2. check if a substitution contains a malicious forward reference and reject
the invalid input (hard to traverse AST at this point; substitutions are quite
common: may affect performance; hard to clearly detect loops at this point)
3. detect loops in ReferenceType::collapse() (cannot reject the input)</pre>
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